Mechanized area controller

ABSTRACT

Traffic control systems and methods to improve safety are disclosed. The systems, in some example aspects, include a first magnetic field generator mounted over an aisle for generating a first zone magnetic field defining a first zone. The methods, in some example aspects, include generating a first zone magnetic field defining a first zone by a first magnetic field generator mounted over an aisle. Other aspects include generating, and/or including a controller to generate, control signals to reduce the speed of a vehicle, and/or reduce the size of a danger zone.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. application Ser. No.16/214,841, filed Dec. 10, 2018, which is a continuation of U.S.application Ser. No. 15/672,516, filed Aug. 9, 2017, which is acontinuation of U.S. application Ser. No. 14/151,056 filed Jan. 9, 2014,which claims priority to U.S. provisional application 61/750,551, filedJan. 9, 2013, which are hereby incorporated by reference in theirentirety.

BACKGROUND

This disclosure relates generally to proximity detection systems at worksites, and in particular to proximity detection systems that allowsystem response to be altered depending on the particular operationalsituation.

In industrial settings, personnel are often required to work near movingmachines and vehicles. Much too often, workers are injured while doingtheir jobs. As more equipment is used and as that equipment has becomelarger and more powerful, and as the operations have become morecomplex, many of the injuries and fatalities result from workers beingstruck or crushed by the moving machines/vehicles or by collisionsbetween vehicles.

Many methods have been devised to warn people against being struck,pinched, crushed or otherwise harmed by vehicles and mobile equipment.Unfortunately, the systems that have been devised to help protect peopleand property in these industrial operations, such as proximity detectionand collision avoidance systems, have usually not been very effective. Anew proximity detection system was developed and successfullydemonstrated for use on continuous miners, as disclosed in U.S. Pat. No.7,420,471 (the '471 patent), U.S. Pat. No. 8,169,335 (the '335 patent)and U.S. Pat. No. 8,232,888 (the '888 patent), and U.S. patentpublications 2009/0322512 (the '512 publication) and 2010/0271214 (the'214 publication), which patents and publications are herein referred tocollectively as the “Frederick patents,” the disclosures of which areincorporated herein by reference in their entireties. An objective ofthe '471 patent is to help prevent the crushing or pinning of personnelwho are remotely controlling a continuous miner, and to help protectother personnel assisting in use of the continuous miners. The '471patent also envisions to provide protection to personnel from othertypes of mobile equipment and machines. The system of the '471 patentemploys a magnetic marker field and an active architecture thatincorporates two-way communication between the worker and the machinethe worker is near. Warnings are given to workers that are too close tothe miner. Warnings are also provided to the operator of the machine.Provisions are made to immobilize the equipment until personnel wereable to reach a safer position.

The magnetic fields used in the '471 patent system oscillate at lowfrequencies and can be effectively used to mark off warning zones,danger zones and silent zones. Although the maximum practical range ofsuch low frequency magnetic fields may be as much as one hundred feet,in most applications that is more than is needed or desirable for mostequipment. Typical very large off-highway haul trucks would probably bebest served with a warning zone in the range of eighty feet and a dangerzone in the range of thirty to forty feet. In some applications, such asremotely controlled continuous miners, it is necessary for the operatorto remain within a range of five to ten feet much of the time in orderto maintain good visual contact with the machine and the immediatesurroundings. The zones are shaped to be longer in the direction oftravel or movement but less in directions perpendicular to the directionof travel. In underground mines, the low frequency magnetic fields passthrough earth formations unimpeded so that a worker that is around acorner, not in line of sight, or otherwise obstructed, will still bevisible to the marker field. These magnetic fields do not radiate fromantennas but simply expand and contract around the element that producesthem, and are well suited for marking boundaries between silent zonesand warning zones.

The invention is particularly applicable to work sites that requirepersonnel to be in close proximity to various hazardous elements, suchas machines, mobile equipment, remotely controlled machines, andoperated vehicles. Such work environments may include locations that areinherently dangerous and should be avoided or entered only with greatcaution. Examples of such work environments are surface mining,underground mining, sand and gravel operations, road construction,warehouses, shipping docks, coke plants, factories, industrial sites andother environments. Hundreds of people are killed each year in the U.S.in such work environments. Workers are sometimes struck, pinched,crushed or otherwise harmed while performing their jobs in suchenvironments. Collisions between the various elements at the work sitesneed to be avoided also to avert property damage.

Referring now to FIG. 1, there is illustrated a simplified example of awork site in which a proximity detection system is implemented. FIG. 1shows a truck 304 on which a magnetic field generator (MFG) 81 ismounted. The magnetic field generator 81 generates a magnetic field 92that surrounds the truck 304. The edge of the magnetic field 92generated by the magnetic field generator 81 corresponds to a magneticfield strength defining the border of a Warning or Danger Zone (safetyzone) surrounding the truck 304. A worker 301 within the boundary of theWarning or Danger Zone 92 is in potential danger from being struck orotherwise injured by the truck 304. The worker 301 carries a personalalarm device (PAD) 60. If the worker 301 and, correspondingly, thepersonal alarm device 60 are within the magnetic field 92 created by themagnetic field generator 81, the personal alarm device 60 detects thepresence of the magnetic field 92 and issues a visual or audio warning.In embodiments of the magnetic field warning system, as detailed in the'888 patent, multiple magnetic field generators 81 may be used togenerate Warning and Danger Zones having a complex shape around thetruck 304 or other equipment or areas. These zones may be adjusted inboth size and shape. In addition, safe zones may be designated near thetruck 304 in which a personal alarm device 60, while within the magneticfield 92, does not generate a warning signal to the worker 301.

FIG. 2 is a diagram of the personal alarm device 60 and the magneticfield generator 81 of the proximity detection system of FIG. 1. Amagnetic field generator 81 is contained within a housing 80 andincludes an amplifier 84 connected to a ferrite core 90, inductor 86 andcapacitor 88. In addition, the magnetic field generator 81 is connectedto a power source 83 that provides the power to operate the magneticfield generator 81. The amplifier 84 is connected to and controlled by acontroller 82. The ferrite core 90, inductor 86 and capacitor 88generate a magnetic field 92 in response to an input voltage from theamplifier 84. The amplifier 84 is controlled by the controller 82 whichcontrols the voltage and current outputs of the amplifier 84. Thecontroller 82 is also connected to a receiver 96 and warning system 98.The receiver 96 is connected to an antenna 94 which receives an inputsignal 76 from a personal alarm device 60. The antenna 94 conveys thesignal 76 to the receiver 96 which passes the signal 76 to thecontroller 82. Upon receiving the signal 76 from the personal alarmdevice 60, the controller 82 directs the warning system 98 to issue awarning. In one embodiment, the warning system 98 may issue an audioand/or visual warning. In another embodiment, the warning system 98 maybe capable of terminating the operation of a vehicle to which thewarning system 98 is mounted, for example, the truck 304 of FIG. 1. Themagnetic field generator 81 may also be mounted in a location in whichit is desirable to warn a worker carrying a personal alarm device 60 oftheir proximity to the location.

The personal alarm device 60 has x, y, and z axis magnetic fieldantennas 62 that sense the magnetic field 92 produced by the magneticfield generator 81. The sensed magnetic field signal is passed throughfilters 66 and an amplifier 68 to a signal detector 64. The signaldetector 64 then passes information about the detected signal to acontroller 70. The controller 70 activates a transmitter 72 whichtransmits a corresponding response signal 76 to the magnetic field 92through an RF (radio frequency) antenna 74. In one embodiment, theresponse signal 76 is an RF signal. The personal alarm device 60 ispowered by power source 71. The personal alarm device 60 is carried bythe worker 301 (FIG. 1) in order to provide the worker with a warning oftheir proximity to a magnetic field generator 81.

In such work sites, it is often necessary for workers and vehicles, suchas fork lifts and lift trucks, to share the same work space. Forexample, workers may need to work near machines that must be servicedwith supplies, materials must be delivered to worker's areas by forktrucks, etc., or vehicles may need to retrieve materials, finishedproducts, or waste products from machines where workers are employed.However, it is also often the case that workers and vehicles must sharea space, but should not concurrently be in this space. Thus, there is aneed for new capabilities that will retain the safety benefits of theknown proximity detection devices while allowing how MFGs and PADsrespond to the operational situation to be altered, e.g., in order toensure that workers and vehicles are not concurrently in the same areaor in order to avoid false alarms in a situation where it is desiredthat the worker be near the vehicle/equipment.

Proximity Detection Systems and Collision Avoidance (PDS/CA) systems arebeing implemented on Powered Industrial Trucks such as Fork Trucks andClamp Trucks, conveyors, haulers, personnel carriers, a wide variety ofmining equipment, and other equipment. These safety systems typicallygive warnings to operators that the machine or vehicle is a threat tothe safety of someone and gives warnings to those being threatened. Theyalso help avoid collisions between vehicles, between vehicles andobjects, or to keep the vehicles out of certain areas. They may alsorecord information related to accidents or accident-prone conditions, ormay even transmit information real-time for monitoring and tracking. Thecurrent disclosure is related to providing safety protection in highlymechanized areas and will normally be used in support of or incombination with PDS/CA systems.

Although some currently available PDS/CA systems are a very effectiveand practical means for reducing “hit-by” accidents in most parts of afacility, there may be highly mechanized areas where specialcircumstances may cause PDS/CA systems to be ineffective or to not beusable. An example would be where there are large fixed-place machinesbeing operated by workers, mobile machines working around the fixedmachines, pedestrians working in the area, and other personnel having topass through the area for other reasons. Loading docks where pedestriansand fork trucks must work closely together can also create complexoperational scenarios. Another example would be intersections where bothmachines and pedestrians must frequently cross paths. Another case iswhen fork lifts go between storage racks to store or retrieve pallets ofitems from the racks and workers are in the same area, even on theopposite side of the racks. Magnetic fields produced by a PDS/CA systemmay extend through the racks and warn a pedestrian or other mobilemachine when they are perfectly safe, separated from the fork truck bythe racks. The use of PDS/CA systems in these areas, and many othersituations that could be listed, may be confusing, may even bedisruptive to normal work and can seriously impact production. Thecentral problem is that many alarms are given and safety is notsignificantly improved.

Although these mechanized locations usually involve only a very smallpart of a facility or industrial operation, sometimes they are thehighest “hit-by” risk areas so that protection is greatly needed there.The current disclosure provides a mechanized area controller (MAC) forpedestrians and mobile machines in mechanized areas to be betterprotected while to a lesser degree or not at all impacting productivityor causing confusion.

There is a related reason that the present disclosure may be veryimportant for some industrial settings. Even though PDS/CA systems canbe successfully deployed throughout the majority of a facility,pedestrians and mobile machines that are effectively using those systemsmust from time to time, if not frequently, enter those relatively smallareas where these systems would either be ineffective or disruptive toproduction and confusing. Therefore, facility managers can bediscouraged from using PDS/CA systems to provide added safety for theirworkers and equipment in the large majority of their facility because ofthe complications in one or a few small areas. Yet, after extensivesteps have been taken to try to eliminate “hit-by” accidents by moreconventional means, employing training, procedures, signs, markers, andlights, accidents still occur and the managers seek a solution. Amanager may consider taking drastic actions such as installing governorsto slow down all mobile machines at all times. Slower speeds may reducethe frequency of some types of accidents but slower speeds may have asevere impact on production. Faster machines do more work. The presentdisclosure makes it more practical to deploy PDS/CA systems throughout afacility by making the PDS/CA system more useful and usable in even themore complex situations. The present disclosure utilizes system elementsthat cooperate with each other, and provide or interact with safetydevices on mobile machines and safety devices being carried bypedestrians. These devices also provide signals to activatefacility-provided warning systems. Although PDS/CA systems currently inuse in mining and other industrial operations are described in detail inthe Frederick patents, as well as in commercial literature, a briefreview of key functional features of a PDS/CA system should be helpfulto understanding this invention.

An example of a situation where PDS/CA systems are known to be effectivewould be a person walking behind a fork lift, not being noticed by theoperator, the person being hit when the fork truck backed up. Or, apedestrian steps out from behind an object into the path of a forktruck. Although training, procedures, and passive safety measuresgreatly improve safety, there still are thousands of personnel who areseriously injured by fork trucks in the US each year by simplesituations. About 100 personnel are killed each year in the US, by forktruck accidents. Technology, such as PDS/CA is required to makesignificant reductions of “hit-by” accidents.

FIG. 4 is a diagram of a more complicated work site 100 in a warehouse,showing two fork trucks 101, 103 and a pedestrian/worker 102, where anaccident can occur. Although the driver of Fork Truck 101 can easily seethe pedestrian 102, and will almost always avoid hitting the pedestrian102, sometimes the pedestrian may make an unexpected change in directionand be hit. The operator of truck 103 however cannot see the pedestrian102 because his view is blocked by tall storage racks 104. If thepedestrian 102 were to step out in front of the truck 103 and theoperator of truck 103 were to be distracted by other tasks or otherevents, then the pedestrian 102 might be hit. If both trucks 101, 103are moving toward the junction where they will cross paths, they couldcollide. The operator of truck 101 might be distracted in passing thepedestrian 102 and drive his/her truck into the path of truck 101. Manyother scenarios could occur with this kind of situation that couldresult in a pedestrian being hit or of trucks colliding.

Note the elliptical dashed line 107 around Fork Truck 101 and thesimilar line 108 around Fork Truck 103. These lines represent themagnetic field strength defining Warning level safety zones that areproduced around these vehicles by the PDS/CAs on each truck. Commercialliterature shows that a typical size of these elliptical fields at thewarning level may have a major radius of about 44 feet. The settings inPersonal Alarm Devices for the Danger level would normally be set tocorrespond to a major radius 60%-70% of the major radius for the warninglevel. This range may be adjusted for differing machine sizes andspecial operational considerations. The minor radius of line 107 willalways be about 80% of the major radius, or about 30 feet in this case.The parameters are similar for line 108. The most effective tool forestablishing these zones is using magnetic field generators 109, 110.Other techniques such as Radio Frequency transmissions are sometimesused but are less precise and less reliable. When the magnetic fieldrepresented by line 107 reaches sufficient strength at the pedestrian102, the Personal Alarm Device (PAD) carried by the pedestrian 102senses the proximity of the truck 101 and produces visible and audiblealarms to the pedestrian 102. These alarms can have more than one leveland may depend on magnetic field strength, the first being an initialwarning and a second being a more intense warning signaling a greaterdanger. At the time the pedestrian 102 is warned, the operator of truck101 is also given an alarm. Thus, both the pedestrian and the truckoperator have warnings to give them an opportunity to take action toavoid an accident. Similarly, the magnetic field around truck 103 willalso warn the pedestrian 102 and result in a warning to the operator oftruck 103. Likewise, the operators of the two trucks 101, 103 will eachbe given a warning that they are approaching each other. The details ofhow these warnings are provided are included in the Frederick patentsand commercial literature. The current invention is a system thatmanages, coordinates, and controls the movements of personnel andequipment in areas which are mechanized, and incorporates the inherentcapabilities of well-designed PDS/CA systems.

It should be noted that the use of low frequency magnetic fields toestablish the safety zones has been shown to the most effectiveavailable technology and will be assumed as the type of PDS/CA systemincluded in and/or used in cooperation with the current disclosure. Thisinvention could be adapted for use with other types of PDS/CA systems,such as RFID, by making certain changes and additions, if such othersystem technologies were to be improved to have sufficient precision andreliability.

The MAC could also be used in robotic areas where some or all of theoperators are replaced by computers and pedestrian functions areperformed by robots. Whether the operator is a person or a computer withappropriate sensors will not have a material effect on the functionalvalue of the MAC system. Higher levels of automation would affectdetails about how warnings were issued and interpreted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an exemplary work site at which a proximitydetection system is implemented.

FIG. 2 is a diagram of a personal alarm device and magnetic fieldgenerator of the proximity detection system of FIG. 1.

FIG. 3 is a diagram of an exemplary embodiment of the multi-functionalstrip zone (MSZ) device of the disclosed embodiments.

FIG. 4 is a diagram of an exemplary work site at which a PDS/CA isimplemented.

FIG. 5 is a diagram of an exemplary work site at which a mechanized areacontroller (“MAC”) may be implemented.

FIG. 6 is a diagram showing an exemplary implementation of MACs of thedisclosed embodiments in the work site of FIG. 5.

FIG. 7 is a diagram showing an exemplary implementation of MACs of thedisclosed embodiments at another exemplary work site.

FIG. 8 is a schematic diagram of an exemplary embodiment of MAC fieldgeneration.

FIG. 9 is a diagram of an exemplary embodiment of a MAC device of thedisclosed embodiments.

FIG. 10 is a diagram of an exemplary embodiment of a MAC-V device of thedisclosed embodiments.

FIG. 11 is a diagram of another exemplary embodiment of a MAC device ofthe disclosed embodiments.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The various embodiments described herein are particularly applicable towork sites that require personnel to be in close proximity to varioushazardous elements, such as machines, mobile equipment, poweredindustrial trucks, remotely controlled machines, and operated vehicles.Such work environments may include locations that are inherentlydangerous and should be avoided or entered only with great caution.Examples of such work environments are surface mining, undergroundmining, sand and gravel operations, road construction, warehouses,shipping docks, coke plants, factories, industrial sites and otherenvironments. Workers are sometimes struck, pinched, crushed orotherwise harmed while performing their jobs in such environments.Collisions between the various elements at the work sites need to beavoided also to avert property damage.

In accordance with an exemplary embodiment, an additional device isprovided in the proximity detection system which interacts with the MFGson the vehicles and with the PADs worn by the workers, in order to alterhow they respond to the operational situation, e.g., in order to ensurethat workers and vehicles are not concurrently in the same area or inorder to avoid false alarms in a situation where it is desired that theworker be near the vehicle/equipment. As described herein, thisadditional device is referred to as a multi-functional strip zone (MSZ)device.

With reference to FIG. 3, the MSZ device 100 includes a support tube 105that is suspended above a work area in which workers and vehicles shouldalternately share the space, but should not concurrently be present. Thesupport tube 105 may be made of any material that does not promoteinterference with the electronics of the system and the generation andpropagation of magnetic fields, for example, any non-metallic material,for example, PVC pipe. The support tube 105 supports a wire loop 110(shown with dotted lines) and an electronics module 115. Alternatively,wire loop 110 may be contained inside the support tube 105. The wireloop 110 and electronics module 115 act to produce a magnetic field (ofcontrollable sizes and timing, based on, for example, the wire length,path, configuration and/or voltage provided thereto) or to act as anantenna to detect magnetic fields, for example, fields produced byproximity systems on vehicles, PADs or other field generating devices.The circuitry of the module 115 may be similar in applicable respects tothe circuitry of the generator 81 and alarm device 60 (FIG. 2), exceptthe loop replaces the ferrite core 90 and the antennae 62; and thecircuitry of module 115 provides for coordination of functions of thealarm device circuitry and magnetic field generator circuitry, forexample by way of a connector (not shown) between the alarm devicecircuitry and magnetic field generator circuitry. Additionally, asillustrated, the electronics module 115 controls the wire loop 110 toact, alternatingly, as both an MFG and as an antenna to detect pulsesfrom other magnetic field generators in the area near the MSZ device100.

In one embodiment, in operation, generally, the MSZ device 100 generatesa field that defines a “stay-out zone,” in which trucks and workers maynot be present at the same time. When a truck approaches the “stay-outzone,” the truck will not be warned if there are no workers in the“stay-out zone.” However, if a truck attempts to enter the “stay-outzone” when a worker is present, or vice versa, a warning alarm will beactivated, e.g., a visible or audible alarm, such as area-wide warninglights 130. The MSZ device 100 operates in a monitor mode if there is notruck in, or approaching, the “stay-out zone.” However, once a truck isdetected as approaching the “stay-out zone,” the MSZ device 100 willbegin to ping the PADs that might be in the area. If there are no PADsin the “stay-out zone,” the MSZ device 100 will alternate betweenverifying that the truck is still in the “stay-out zone” and verifyingthat there are no PADs in the zone. If a worker is in the “stay-outzone” when the truck arrives, or if a pedestrian enters the “stay-outzone” while the truck is in the “stay-out zone,” then the MSZ device 100will echo to the MFG on the truck with a danger echo and follow up witha burst, etc. The MSZ device 100 will continue to confirm that thisdanger state exists and will drop the danger echoes once the truck orthe pedestrian leaves the “stay-out zone.” The implementation of thePING-ECHO communication of the MFGs and PADs is described in more detailin the Frederick patents.

In one particular embodiment of the MSZ device 100, which has beentested by the inventor, the support tube 105 may be 100 feet to 200 feetlong. For example, the support tube 105 may be constructed with 10 footlong sections of 1½ in diameter, schedule 40 PVC pipe that are connectedtogether. It is believed that the MSZ device 100 may be implementedusing a support tube 105 up to 1000 feet long or longer. The wire loop110, attached to the exterior of the support tube 105 using wire ties orother means, may be a #10 AWG insulated copper wire, in order to producea loop that is the length of the support tube 105 and approximately 1¾in in cross-section. The wire 110 may be attached on opposite sides ofthe tube 105 to provide separation of the wire from itself. Increasingthe separation increases the size of the magnetic field generated withthe wire 110. Alternatively, the wire 110 may be positioned inside thetube 105 using a lattice wire (or otherwise providing wire separation)to form the wire loop 110. The ends of the wire loop 110 are connectedto electronics module 115, which is installed into a “T” section of PVCpipe near the center of the support tube 105. Alternatively, the modulemay be mounted at another location along the tube 105, or within thetube 105, with or without a T-section.

The electronics module 115 contains capacitors that have a reactancevalue equal in value to the effective reactance of the wire loop 110 onthe support tube 105, so that the combined circuit resonates at 73,000Hertz. A power supply 120, e.g., 12 VDC, is provided to the electronicsmodule 115 to drive the electronics module 115 and the wire loop 110. Aheavy duty wall adapter may be used for this purpose. Atransformer/relay unit 125 is provided that sends, for example, 24 VACto the electronics module 115 which is returned to the control relaythat sends power to the area-wide warning light 130. If applicable, asecond and third 24 VAC signal may be sent out to control a danger lightand a green light. The circuitry configuration allows driving the tunedcircuit with pulses of current at the rate of 73,000 Hz and allows thecircuit to detect pulses from other MFGs in the area near the MSZ device100. These multiple functions are accomplished with the same MSZ device100 by alternating between these functions using manual switching orautomatic switching to accomplish the same. Magnetic fields produced bythe MSZ device 100 can, not only, be pings of 73,000 Hz that can bedetected by standard PADs, such as those described in the Frederickpatents, but also can be fields that will result in the establishment ofsilent zones for PADs, as described for example in the '888 patent orthe '214 publication. When 12 VDC are provided, a magnetic field dangerzone of about 57 feet surrounding the wire loop 110 can be produced. Thesize of the magnetic field can be adjusted by controlling the voltageused to generate the 73 kHz pulses to drive the field generating circuitor by controlling the width of the pulses. The field size can beautomatically changed by the microcontroller during operation asdetermined by the logic in the microcontroller.

One example of an industrial environment in which the MSZ device 100 ofthe disclosed embodiments may be employed is for the implementation ofsafety zones near the wet end of corrugation machines, which are used,for example, for converting paper into corrugated roll or board. Forktrucks and clamp trucks must occasionally enter the area around the wetend of the corrugation machines. A “stay-out zone” area for workers mustbe activated behind the corrugation machine when such a truck isapproaching. This “stay-out zone” includes the paper rolls that havebeen positioned to be ready for use in the corrugation machine. An MSZdevice 100, as described above, is used to accomplish this “stay-outzone,” as is further described. The MSZ device 100 may be located abovethe “stay-out zone.” For example, the MSZ device 100 may be mounted at aheight of approximately 11 feet, so as to not be in the way of machineryand workers moving through the area. For example, in a factoryenvironment, the device 100 may be suspended from the ceiling or otherstructure using wires or other hangers.

Each truck is equipped with a standard MFG and continues to function inthe same manner when in the area around the wet end of the corrugationmachines as when in the warehouse generally. Each of the workers may beequipped with a PAD for use throughout the facility where movingvehicles are being operated, or areas that are hazardous to pedestrians.Each of the vehicles may be equipped with a vehicle alarm device (VAD)for use throughout the facility including areas where vehicles shouldnot enter. The PAD/VAD is configured such that it can be used anywherein the facility without being changed, including at the wet end of thecorrugation machines.

When a truck approaches the “stay-out zone,” an area-wide alarm lightmay flash intermittently, e.g., a triple flash every 10 seconds, untilthe truck leaves the area to alert workers that a truck is in the areaand that they should not enter. At the same time, the truck operator maybe given a warning in the vehicle cab by the vehicle alarm device, e.g.,visible and/or audible warnings, that the truck is entering a worker“stay-out zone.” Alternatively, the truck operator may not be given thewarnings in the vehicle cab if there are no workers in the “stay-outzone.” When a worker enters the “stay-out zone,” the warning light inthe vehicle cab in the zone may change from one state to another, suchas for example, from flashing (or silent) to a constant red light.

Alternatively, when a truck approaches the “stay-out zone,” thearea-wide alarm light would not activate if there are no workers in the“stay-out zone.” And would activate if a worker enters the “stay-outzone.”

Alternatively, when a truck approaches the “stay-out zone,” an area-widegreen light may illuminate if there are no workers in the “stay-outzone.” At the same time, the truck operator may be given a green lightin the vehicle cab by the vehicle alarm device, indicating that thetruck is entering a worker “stay-out zone” where there are no workers.

If a worker enters the “stay-out zone” while a truck is in the area, thearea-wide alarm light will flash continuously, until either the workeror the truck leaves the zone. A very loud horn could also be sounded toalert workers in the area that a truck has entered the “stay-out zone”And the pedestrian must exit the stay-out zone. While each worker isequipped with a PAD, the audible alarm of the PAD is likely unable to beheard at the wet end of the corrugator machine, and thus the worker mustrely on the area-wide alarm light and/or horn to alert him that a truckis entering the “stay-out zone.”

Additionally, if the worker is wearing headphones, such as forcommunicating with other workers, the PAD may be connected to theheadphones to send the audible alarm signal to headphones. Circuitry maybe provided to override any other signal being sent to the headphonesthat may interfere with the alarm signal. In some embodiments, anoperator of the corrugation machine may need to remain in an area nearthe machine, even when trucks are approaching the machine. A silent zonecould be placed near the machine, so that the area-wide alarm light andthe machine operator's PAD would not give a warning as long as themachine operator remains in the silent zone.

While the MSZ device 100 has been described herein as implementing a“stay-out zone,” the MSZ device 100 could also be used to implement“safe zones.” For example, an MSZ device 100 as described may bearranged above a location that is safe for people but where trucks orother machines may be passing by and warnings are not desired. Anotherexample is to implement a “safe spots,” in which a worker can stand(e.g., a mat on the floor) and an MSZ device 100 in the “spot” willsilence the worker's PAD. This “safe spot” allows trucks to come into anarea where workers must work, when necessary—the worker can step asideonto a safe spot, which has been positioned so that it cannot be reachedby a truck, and once the truck clears the area, the worker can stop offthe safe spot and return to work.

A MAC may include an MSZ device. Each MAC includes elements that cancommunicate to PDS/CA systems on machines and to PADs carried bypedestrians, by use of magnetic fields and has at least one UHF receiverthat can receive RF responses from PADs and PDS/CA systems. Twoembodiments are disclosed, MAC-A and MAC-V. The basic difference betweenthese configurations is in the manner by which the magnetic fields areproduced in order to have the fields where needed and in the preferredorientation. The MAC-A version uses a loop of wire running lengthwisearound the long support tube which produces a linear shaped field aroundthe loop/tube, as will be described later. The MAC-V version typicallyhas two ferrite generators each of which produces a smaller magneticfield at each end of the support tube, which will also be describedlater. It should also be understood that the features of a MAC-A and aMAC-V can be incorporated into a single unit, where needed, but it iseasier to explain the functions by keeping the two types somewhatseparated in the following explanations, since the chosen illustrationutilizes the two versions. However, since these two embodimentscooperate together as a system, the discussion of one of them mayinclude mention of the other. The term “MAC” is used to also apply toMAC-A, MAC-V and/or other versions.

In order to better illustrate how the MAC may be effective in highlymechanized areas, an industrial application has been selected which isoperationally challenging. By showing how the MAC-A and MAC-V would beused in this complex work environment, its powerful features can bedemonstrated.

Corrugated paper products are widely used for making items such asboxes. The machines that are used to manufacture the corrugatedmaterials are large and involve a complex combination of men andmachines. A typical machine is over 150 feet long, requiring multipleworkers be stationed around the corrugator machine, and requiring thatit be supplied with large rolls of paper, as well as other materials.Maintenance personnel must have access to the machine. Records must bekept, including records of information on the rolls of paper. Scrappaper and other items must be continually removed from the area, usuallyby a fork truck. Clamp trucks are used to transport rolls of paper froma warehouse area to the machine and to be positioned on an elevator thatmoves the rolls into the machine as needed. Other personnel must movethrough the area and in adjacent work spaces. A rail-type transfer caris typically operating at the periphery of the work area. The clamptruck that delivers and positions the paper and the fork truck are knownto hit pedestrians and to push or roll paper into workers. It isessential that the mobile machines and the pedestrians share use of thearea behind the corrugator. The corrugator is very loud, requiring theuse of hearing protection. Workers that routinely work in the noisy areawear double protection, plugs and muffs. With the inability to hear, andwith the distractions from the many activities, the pedestrians arevulnerable. Accident statistics confirm the perceived danger.

An AREA 210 in FIG. 5, identified by hashed lines, must be used bypedestrians (202-206) and others not shown, by clamp trucks 207, 214 andby fork trucks 208, 209. Personnel not shown include maintenancepersonnel, managers, safety personnel, warehouse workers, visitors, etc.The clamp truck and the fork trucks may not always be the same machinesfrom day to day. Also shown is a Transfer rail car 211 which movesmaterials. For purposes of this discussion, it is assumed that all themobile machines and all personnel are outfitted with PDS/CA systemssimilar to those described in the Frederick patents.

After some study, it can be recognized that this is a complex operation,safety-wise. Not only must the pedestrians work in close proximity tothe mobile machines but they must even share the same space. Obviously,the only way to safely share the same space is to ensure that thepedestrians and the machines do not try to share the same space at thesame moment in time. The challenge is greater than what might berecognized at first glance because, for productivity reasons, it isdesirable to allow pedestrians to be within this large area at one endwhile a mobile machine is at the other end. Workers 202, 203, 204 whoare adjacent to the machine, not actually in the shared area 210, aresafe so long as they do not enter the shared area 210. It is importantthat they not be warned when they are actually safe (such as by seeing awarning light that is not meant for them), even though they may berelatively close to machines that are in the area. Similarly, it isimportant that the operators of the clamp trucks 207, 214 or the forktrucks not be warned about the close proximity of workers who areactually in no immediate danger. Another danger is to pedestrians whoare passing through the noisy area when a clamp truck suddenly entersthe area through one of the aisles 212, 213. Many specific situationsand scenarios could be cited where pedestrians could be in danger ofbeing hit in the shared area and in the aisles A1 (212) and A2 (213).The MAC system, including the MAC-A and MAC-V, attempts to address allof these concerns.

In general terms, there are at least four major requirements for the MACof the illustrated embodiment of FIG. 5. (1) Control the access to theshared area so that pedestrians or machines can be in the area but notboth at the same time. (2) Control the speed of the clamp truck enteringthe area without limiting its speed as it leaves the shared area or atother locations in the facility. (3) Modify the operation of the PDS/CAsystem so that it will not produce nuisance alarms when entering theshared area but quickly return to normal operation upon exiting thearea. (4) Control the movements in such a way to reduce confusion and toencourage orderly movements.

It is assumed that respective PDS/CA system components are installed onall of the mobile machines and the pedestrians. One MAC unit manages thesharing of the AREA 210. A second version of MAC (MAC-V) measures thespeed and direction of clamp trucks approaching or leaving the AREA 210via an aisle. In the specific case illustrated in FIG. 6, there are twoaisles so that a third MAC (a MAC-V) is used there. The MACs providesignals to the PDS/CA systems, using magnetic fields, and issue signalsto activate facility warning systems. Less complex applications may notrequire all of these elements. It should be pointed out that there aremany variations to the example cited above. For example, there may beonly one aisle or three aisles rather than the two shown. There may beonly one clamp truck serving the operation with rolls of paper 250. Theoverall dimensions and arrangements may be different. But, most of thebasic challenges will be present in most plants that have a corrugatormachine 201. Note that the corrugator 201 extends above the floor planshown in FIGS. 5 and 6 forming (between corrugator 201 portions 255)aisles 252 where workers and/or vehicles may enter. Also other portions261 of the corrugator 201 intersect with the work floor in the shadedarea 210. Corrugator 201 may extend above the aisles 252 and otherareas.

Referring to FIG. 6, the hashed lines in FIG. 5 have been replaced withthe wavy, sinusoidal lines to indicate that magnetic fields have beengenerated by MAC-As 302, 303, 304 to fill the AREA 210. Also, MAC-Vs305, 306 have been placed above each aisle 212, 213.

The three MACs positioned above the AREA 210 generate pulses ofoscillating low frequency magnetic fields so as to fill the AREA 210.These fields will be detected by the CA modules on the mobile machinesif they are within the AREA 210. These fields will also be detected bythe PADs carried by any pedestrians if in the AREA 210. If both mobilemachines and PADs are in the AREA 210 at the same time, highly visiblered lights will begin flashing around the AREA 210, until either thepedestrians or the machines leave. However, instead of making the MACinto a single unit, running the length of the AREA 210, it is made intothree segments 302, 303, 304. Doing so may better accommodate a truckbeing in one end of the area 210 while pedestrians are in the other end.Some facilities may have a smaller shared area so that there would onlybe one or two MAC segments. In order to minimize confusion, anapproaching clamp truck, delivering another roll of paper, will resultin a highly visible yellow light being flashed to alert the pedestriansthat a clamp truck is approaching. The sensing of an arriving clamptruck will be sensed by the MAC-Vs 305, 306 above the aisle(s) 212, 213.Facility warning lights are activated by the MACs and MAC-Vs as neededto encourage an orderly movement of pedestrians as the trucks move fromone portion of the AREA to another.

For example, an operator on a truck 207 that is approaching the sharedarea needs to know if there is a pedestrian in the AREA 210 or in thepart of the shared area to be entered by the truck 207. If there are nopedestrians in the AREA 210, a green light 323 in the traffic controlunit 329 will be turned on at the end of the aisle 212 by the MAC-1 302and the operator can drive into the area. If a pedestrian is present ina portion of the AREA 210 to be entered by the truck 207, a yellow light324 in the Traffic Control Unit 329 at the end of the aisle 212 will belit. Seeing the yellow light, the operator of the truck 207 shouldeither stop the truck until the area is clear or slow the truck 207 andlook carefully until the pedestrians vacate the AREA 210, depending uponthe strategy used by the safety director.

Since pedestrians will be warned in a highly visible manner to vacatethe AREA 210 before the truck 207 arrives, the danger of being hit hasbeen essentially eliminated. However, if their PADs and if the warninglights on the truck 207 give warnings even after they know that thedanger has been removed, these nuisance alarms will drastically degradethe effectiveness of the system and can create confusion. It isimportant for workers to be assured that when warnings are given, actionis required. False warnings and nuisance alarms must be eliminated. TheMAC inhibits nuisance alarms from being caused from misdirectedinstructions, by sending a specially coded set of pulses via themagnetic field into the AREA 210 which are then sensed by the PDS/CAsystems. The micro-controller in the PDS/CA system either shrinks orstops producing the magnetic fields on the machine, depending upon thechoice coded into the software. The choice between these options dependsupon other peripheral factors. When the trucks leave the AREA 210, theirPDS/CA systems will resume operations as required for entering thewarehouse where large safety zones around the machines are desired.

It is worth noting that use of the magnetic field to modify the way thePDS/CA systems function has the important benefit of only affecting themachines that are in the field, which is precise and stable. RFtransmissions could be used except they are difficult to control andthey are prone to propagate outside the AREA 210 and affect theoperation of nearby machines that are not in the AREA 210. Confusing orfalse indications or unintended actions are unacceptable for a safetysystem or, otherwise, users will lose confidence in the system andignore its warnings.

Steps must be taken to control the approach to the AREA 210 by thetrucks. A Traffic Control Unit 329, mentioned earlier, having a set ofthree lights, is positioned at the end of the aisle 212 leading to theAREA. One light 323 is green to indicate that there are no pedestriansin the AREA 210 ahead. Another light 324 is yellow and would indicate ifthere is a pedestrian in the AREA 210. A third, red light 325 willindicate if the truck is approaching too rapidly. In addition, as thetruck is approaching there will be two points at which the PDS/CAwarning light on the truck will be flashed. Ideally, this light would bea highly visible type.

The MAC-Vs 305, 306 are positioned above the aisles 212, 213 so thatthey can measure the speed and direction of the trucks. If the truckapproaches at a speed greater than the limit set by the safety director,the sensor on the end of the MAC that is closest to the truck willinitiate a signal to the PDS/CA system on the truck and it will flashthe light a couple of times to warn the operator that the truck needs tobe slowed down. If the truck is still going too fast when its speed ismeasured by the second sensor, then a danger signal will be sent to thePDS/CA system and the warning light will be flashed for an extendedperiod of time to alert the operator and other personnel that the truckis going too fast. While underneath the MAC-V 305 or 306, the safetyzone produced by the PDS/CA will be reduced, if the truck 207 istraveling at less the speed limit for that location. If the truck isexiting, the MAC will detect the outgoing direction and no signals willbe given. It is expected that the truck will quickly resume higherspeeds upon returning to the warehouse and the safety zone produced bythe PDS/CA will return to full size.

If a clamp truck or fork truck is a modern version having an electroniccontrol center, the signals sent to the truck by a MAC to the PDS/CAwill be routed from the PDS/CA to the machine control center to takeactions that are appropriate for the situation. For example, the machinemight be automatically slowed down when notified that the truck ismoving too fast for that specific location. In some instances, ifalready moving at a slow speed, the truck might be automaticallystopped, as is being accomplished on underground mining equipment bysimilar type PDS/CA systems.

The PDS/CA systems and the MAC and MAC-V routinely output a RF data setthat contains information about safety events. This information can bereceived by a RF receiver, sent into a data storage and retrievalsystem. This information can be used to evaluate the events leading upto a hit-by accident, to improve traffic control, or non-safetyfunctions such as evaluating the efficiency and utilization of thetruck.

Many kinds of situations exist in industrial settings where a MAC couldbe useful for improving safety and most are not as complex as thecorrugator example described above. An example is a junction in a plantwhere mobile machines and pedestrians frequently pass. In order to notbe a hindrance to orderly and efficient movements of machines andpeople, it is desirable to alter the operation of the PDS/CA systems onthe machines. FIG. 7 illustrates a four-way junction in which mobilemachines may approach from any direction and pedestrians may be in anylocation, their direction of travel being unrestricted. If multiplemachines, equipped with PDS/CA approach the junction there will bemultiple warnings and potential confusion. If pedestrians are alsopresent, the situation can be confusing, preventing orderly safemovements of all.

Many scenarios can be imagined where accidents can happen at a four-wayintersection where visibility is limited for pedestrians and operators.One solution might be to create a four-way stop but there are reasonswhy this may not be optimum for an industrial setting. Views bypedestrians may be obstructed. The majority of the traffic may be in oneaisle. The majority of the traffic may be pedestrians. Conventions forhighway traffic may not be suitable. Multiple logic options can be usedas preferred by the traffic control specialist, considering the specificneeds at a particular situation. One question to be considered iswhether pedestrians generally have the right-of-way priority overtrucks. Another is whether to give some aisles preference or to givesome directions preference over others. Another question is whether toalways give priority to the first-to-arrive. Most any logic is easy toimplement for a particular junction, by use of MAC, since the output ofdirection and speed can be provided by each MAC to the Traffic ControlUnit 412. The Traffic Control Unit 412 has red 413, 418, 422, 419,yellow 414, 417, 423, 420, and green lights 415, 416, 421, 424 pointingin the direction of each of the four aisles and has a micro-controller.By using the Traffic Control Unit, the movements of trucks andpedestrians can be managed. If a truck is approaching too fast from anydirection all the red lights can be made to flash until the truck hasleft the area. If all trucks are approaching at a safe speed, they canbe commanded to shrink their safety zones to correspond to their lowspeed. Then the logic selected by the safety director can signal passagethrough the junction in an orderly manner. And, the MACs can issue pulsepatterns that will be recognized by the PDS/CA systems as a call forsilencing the warnings so that no one will be receiving warnings, onceall vehicles are stopped or moving very slowly and are being givensignals as to how they should move.

A MAC-A or MAC-V can also be used in congested areas such as loadingdocks. For example, it can give a signal to the PDS/CA systems as forktrucks arrive to automatically reduce the size their safety zones. Also,by changing the pattern of the magnetic fields, the PDS/CA can becommanded to be made silent and/or the PADs in the area can be madesilent. Once PDS/CA systems have been deployed into a facility, MACs canbe installed into those areas where it is desirable to alter theoperation of the PDS/CA functionality and to provide new functions.

In the application shown in FIG. 6, three MACs are positioned at 11 feetabove the floor to give room for clamp trucks and fork trucks to passbeneath. The MACs may be suspended from the ceiling or attached to otherstructures. The height of the MAC may be higher or lower, but should behigh enough to allow room for work activity to be conducted beneath theMAC without hitting it, but should not be so high so that the MAC'sfunction is unacceptably adversely affected. The primary function ofthese three MACs is to control the AREA 210 to prevent pedestrians andmobile machines from being in the same part of the AREA 210 at the sametime. In the chosen illustration, it is desirable to allow trucks to beat one end of the AREA 210 while pedestrians can be in the other end.

A MAC will typically utilize three methods of communicating with thePDS/CA systems. Refer to the diagram in FIG. 8. A MAC can be suspendedabove a work area, aisle, walkway, or roadway. A loop of wire isattached to a non-metallic support which produces a magnetic field whencurrent passes through the loop. The magnetic field lines areessentially in a plane that is perpendicular to the MAC support tube. Ateach end of the MAC-V is another generator that produces a magneticfield that is circular in the horizontal plane. The electronics controlmodule has an UHF transmitter and a UHF receiver, along with other itemssuch as a micro-controller and capacitors to match the reactance of theloop. Magnetic fields produced by the loop are detected by the CollisionAvoidance section of the PDS/CA systems on the mobile equipment. Thesefields are also detected by the PADs carried by the pedestrians. Boththe PDS/CA systems and the PADs respond to the MAC via UHF transmitters.The RF transmissions can also be made in other frequency spectrums ifdesired without changing the functionality of the MAC.

A fundamental element of a MAC is a loop of wire 602 that is attached toa supporting tube 601, made of a non-metallic material such as PVC.Larger wire is desired in order to maintain a high “Q” in the resonantcircuit. A higher Q produces a higher peak voltage which produces ahigher peak current. The size of the field is proportional to the cuberoot of the current in the loop. A suitable low frequency would be lessthan about 100 kHz. A frequency in the general range of about 70 kHz toabout 75 kHz has been found to be useful, being low enough to not beexhibit parasitic coupling to metal objects while being high enough toallow conveying logical instructions in a reasonable time. Some systems,such as HazardAvert® and Hit-Not®, operate at about 73 kHz.

By varying the supply voltage, the size of the magnetic field can beincreased. The example described earlier, showing the three devicesbehind a corrugator machine, which is about 150 feet long, were selectedto be about 50 feet in length each. By measuring the inductance of theloop, the required capacitance can be selected. A person skilled in theart of designing electronic circuits can easily select capacitor sizesand operating voltages to create a magnetic field of the desireddiameter and length. Where needed, the length can be increased tohundreds of feet if the field diameter does not have to be large. Inthis case, the wire loop could be constructed from insulated #10 AWGcopper wire.

An electrical diagram for the MAC is shown in FIG. 9. The linearmagnetic field is produced by switching the power being supplied by theexternal power supply 614 at the 73 kHz frequency to which the resonantcircuit will resonate. The switching is controlled by themicro-controller 606 in the controller module 823. Transmissions oflogical functions or response signals from PADs of workers 202-206 andcollision avoidance (CA) modules 216, 217 are received by a UHF receiver607, via antenna 608. The output from the receiver 607 is fed to themicro-controller 606. Ping echo sequences, as described in the Frederickpatents are controlled by the micro-controller 606. Voltage to theelectronic elements is supplied from external power supply 613. Theseexternal power supplies can be types that are commercially available, ULlisted units, that accept standard 120 VAC, 60 cycle, or other standardpower. Examples would be model DSA-60W-12 power supply, available frommultiple electronics distributors. Highly visible lights in the facilityare powered from facility power though relays inside commerciallyavailable units such as Honeywell Model R8845U switching relay. By usingcommercially available, UL Listed power modules, the MAC units operateentirely on low voltage.

The two other magnetic field generators 307, 308, one mounted at eachend of the MAC, are conventional PDS units of a type currently used forproximity detection except that the ferrite has been oriented with thelong axis of the ferrite being vertical. This orientation produces amagnetic field below the MAC which is circular in the horizontal plane.The ferrite is much smaller than would be required for a PDS system on amobile machine since the required range is much less. In some instances,these two magnetic field generators can be replaced with sensing units,similar to those used in PADs, which will sense the fields produced bythe PDS systems on the mobile machines passing near the MAC.

The following paragraphs will discuss how the logical decisions are madewithin the MAC.

Logical decisions in the MAC are made by the micro-controller 606 in thecontrol module 823. While in the process of preventing simultaneous useof the AREA 210 by both pedestrians and clamp trucks or fork trucks, themicro-controller 606 sends a series of control pulses to the FETs 605 atthe rate of 73 kHz for a duration of 0.003 seconds. The resonant circuitmade up of the loop and the capacitors 604 on the control board, beginsto resonate and produces a magnetic field around the loop. One side ofthe loop 602 is positioned on the support tube 601 on the side nearestthe floor and the other side of the loop is on the top of the supporttube. Each lobe will be somewhat circular with the magnetic lines in aplane that is perpendicular to the tube. The pulse of oscillations thatis produced is called a Ping. Any PAD or PDS/CA within the range of thePing will measure its strength and if strong enough to be at the Dangerlevel, it will send a response, called an Echo, via a UHF transmitter.In the US, the chosen UHF frequency of the Echo might be 916 MHz.

The strength of field chosen as the level for which a decision will bemade can conveniently be chosen to be the same as the level alreadybeing used by the PDS/CA systems, or some other level. The exchange ofPings and Echos establishes that there is either a PAD or a PDS/CAsystem in the AREA, or both. A typical PDS/CA system will perform across check or handshake to ensure that errors are not made in thedecisions. For example, the Ping/Echo may be repeated, following aprecise protocol to confirm the result of the first Ping/Echo sequence.This could be repeated many times, though a total of three sequences hasbeen shown to provide very high reliability in most environments. Thedecision elements must know how many iterations are necessary tocomplete the exchange. In normal PDS/CA operations, the objective wouldbe to complete the required number of exchanges in order to validate anoperational condition. That is not true for the use of the MAC. Apurpose of using the MAC is to take actions to prevent pedestrians andoperators from trying to being in the AREA 210 at the same instant,without giving unnecessary warnings.

In this application, it is important that the MAC not cause the PADs orthe PDS/CA systems to go into a Warning state or Danger state whichwould produce alarms to the pedestrians and to the operator. However, itis important to know whether PADs or trucks having PDS/CA systems are inthe AREA 210. The PDS/CA system assumed for this illustration requiresthat three Ping/Echo sequences be properly completed before a decisioncan be made. Therefore, the MAC only sends a total of two Pings for asequence, not the required three, so that the MAC sequence should notresult in a decision being made to produce an alarm. Additional pairs ofPings will typically be sent each second. By requiring that thedecisions be made when the field strength measured by the PADs or thePDS/CA systems be at the Danger level, the chance of an error for dualPings at such high levels is very small. But, the MAC can actuallyrequire a minimum of two sets of dual Pings or more, receiving thecorresponding Echos, before making decisions. This is possible since theresponse time for this application is less than, for example, inside amine where workers are only a few feet from a machine, and fast responseis essential. Further, the PDS/CA systems within the AREA 210 will becommanded by the MAC to stop generating fields while inside the AREA 210which will further reduce the chance of making an error due toconflicts. It is worth noting at this point that a well-designed PDS/CAsystem will already incorporate various algorithms to analyze thecharacteristics of Pings and Echos to determine if are valid.Incorporating all these steps ensures that false alarms and nuisancealarms will not be caused by erroneous signals.

Once the MAC has verified that there are no PADs in the AREA 210, itsends a signal to operate a relay in the module 616 which will switchfacility power to the green light 621 (or in FIG. 6 green lights 323,326 at the end of the aisles 212, 213 respectively). However, if MACsenses a PAD in the AREA 210, it will turn on a yellow light 620. Once atruck has entered the AREA 210, in any of the three segments under MAC-1302, MAC-3 303, or MAC-3 304, if any PAD enters the AREA 210, themicro-controller in the associated MAC will send a signal to relaymodule 619 which will switch facility power to the set of highvisibility red lights around that segment of the AREA 210 so that allpersonnel will know that both a pedestrian and a truck is present. Thepedestrian should vacate the AREA 210, unless the safety director hasgiven other instructions and procedures.

The three MACs 302, 303, 304, using the above provisions and logic,should be able to prevent simultaneous presence in any of the threesegments of AREA 210 by both one or more pedestrians and one or moretrucks.

Managers of operations of the type being discussed here have expressedthe danger that is caused by clamp trucks approaching or entering acomplex work zone like the AREA 210. Not only is it important to alertthe operator of approaching trucks when there is a pedestrian in theportion of the AREA that the truck is about to enter, it is alsoimportant that the trucks approach slowly. Not only is it possible thata pedestrian might be about ready to enter the AREA 210 but pedestriansare frequently nearby, though not actually in the AREA 210. Due to somelocations not always being visible and due to the high level ofactivity, a pedestrian may step in front of an approaching truck. Forexample, with reference to the truck 207 in aisle 212, to help preventthis from happening, a MAC-V 305 is placed above the aisle 212 tomeasure the speed of the truck 207 moving toward the AREA 210 and togive an alarm if it is moving too rapidly. The micro-controller 606 willalternate generating Pings from the generator 703, 707 in each end 307,308 of the MAC. If a truck is close enough to be in range of the Pings,it's PDS/CA will respond with Echos. As with the MACs over the AREA, itwould be desirable that the echoes at the Danger level be used ratherthan the warning level, because the signal-to-noise ratio is higher atthe danger level. The micro-controller 606 in the MAC-3 module 825 willinitiate an exchange of two more Ping/Echo sequences to confirm that thesignals are valid. Once that has been confirmed, the micro-controller606 will send a data set through the UHF link to notify the PDS/CA thatits speed is to be measured. The PDS/CA will begin to sense the pulsesand measure their strength. The period of time between pulses can bepre-set or it can be transmitted to the PDS/CA via the data set. Forpurposes of this illustration, assume that a total of five pulses aresent, spaced 50 milliseconds apart. The amplitude of the oscillatingmagnetic field being sensed by the PDS/CA will increase inverselyproportional to cube of the distance. Since the distance at which thePDS/CA will sense the magnetic field to be at the Danger level, thedistance is known at which the speed calculations will begin. Themicro-controller will then calculate the speed at which the truck ismoving between each pulse. The four readings will be averaged andcompared to the value set into the MAC for this location. A suitablelimit might be 5 feet per second. Assuming that the magnetic field isadjusted to produce a magnetic that is approximately 20 feet in diameterfor the Danger level, then during the 200 milliseconds from the firstpulse to the fifth pulse, the truck would move one foot. During thattime the strength of the magnetic field would increase approximately bythe cube 10/9, or 37%. This should allow a sufficiently accurate speedmeasurement for most situations. If more accuracy is desired, themeasurements can be fitted to a curve, more pulses can be sent, and/orthe size of the magnetic field can be increased.

The PDS/CA would be programmed to recognize if the speed exceeds 5 feetper second. If so, it would flash the PDS/CA warning lights on the truckto alert the operator that the truck is moving too fast for thislocation.

Since a truck that is near MAC-3 will be detected regardless of whetherit is approaching the AREA or exiting AREA, it is necessary to knowwhich way that it is travelling. While it may be desirable to slow theapproach speed to no more than 5 feet per second, it may also bedesirable to allow a truck that is exiting to begin accelerating up to amore typical speed of 20 feet per second, or more, for work to beperformed in the warehouse. Prior to the MAC-V 305 starting measurementof the speed of truck 207, it would be alternately be generating Pingsfrom by the generator 707 on the other end 308. Logic in themicro-controller 606 determines the direction by comparing timing andfield strength. If a truck is incoming, then the micro-controllerschedules to begin making speed measurements.

There is another important function to be performed. If a truck isdetermined to be approaching, the MAC-V 305 sends an “approach’ signalto the MAC-1 302 through the interconnecting cable. If there is apedestrian in the AREA 210 near MAC-1, then it will turn on a highlyvisible yellow light 314 to alert pedestrians to clear the area. Asimilar response would be happen if a truck was in the other aisle,approaching the AREA near MAC-V 306.

By having the MACs 302, 303, 304 in the example illustrated above,safety in the complex shared AREA behind the corrugator machine would bemade safe by preventing both pedestrians from being in the same area atthe same time, by controlling the approach of trucks, and by givingappropriate warnings to operators and pedestrians. All this isaccomplished without producing nuisance alarms or false alarms. Theoverall effect will be to make the area much safer while not impactingproduction. It also removes the need to take more drastic actions suchas placing governors on machines or of preventing pedestrians from beingin areas where they need to be in order to do their work efficiently.

With reference to FIG. 11, instead of a single support pipe, the MAC mayinclude two support pipes 902, 903 held separated in parallel by spacers910. The loop 918 may be placed inside the pipes and loop back at therespective ends of the pipes (a suitable fitting may be provided) andmay enter and exit the pipes 902, 903 at a control module and fittingsimilar that described with respect to a single pipe embodiment. Thepipes 902, 903 may be a smaller diameter so the two parallel lengths ofthe loop 918 are held at a relatively uniform spacing from one another,such as about two to three inches. A common one-half inch nonconductiveplastic pipe should work.

The MAC described above can be used in numerous other situations wherePDS/CA systems are highly desirable in general but are troublesome whenused in some mechanized areas involving multiple machines and otherpersonnel.

The above description and drawings are only illustrative of preferredembodiments, and are not intended to be limiting. Any subject matter ormodification thereof which comes within the spirit and scope of thedisclosure is to be considered part of the present invention.

What is claimed as new and desired to be protected by Letters Patent ofthe United States is:
 1. A method of proximity detection, comprising thesteps of: generating a first zone magnetic field defining a stay-outzone; generating no warning signal if no workers and no vehicles are inor approaching the stay-out zone; generating no warning signal if noworkers are in or approaching the stay-out zone, and at least onevehicle is in or approaching the stay-out zone; generating no warningsignal if no vehicles are in or approaching the stay-out zone, and atleast one worker is in or approaching the stay-out zone; generating aworker warning signal if at least one worker is in the stay-out zone andat least one vehicle is in or approaching the stay-out zone; andgenerating a vehicle warning signal if at least one vehicle is in thestay-out zone and at least one worker is in or approaching the stay-outzone.
 2. A method as in claim 1, further comprising the step ofgenerating a worker area wide warning signal if at least one worker isin the stay-out zone.
 3. A method as in claim 1, further comprising thestep of generating a vehicle area wide warning signal if at least onevehicle is in the stay-out zone.
 4. A method as in claim 1, furthercomprising the step of generating a worker danger signal if at least oneworker is in the stay-out zone and at least one vehicle enters thestay-out zone.
 5. A method as in claim 4, wherein the worker dangersignal is transmitted to an operator of the at least one vehicle.
 6. Amethod as in claim 1, further comprising the step of generating avehicle danger signal if at least one vehicle is in the stay-out zoneand at least one worker enters the stay-out zone.
 7. A method of claim1, further comprising the steps of: generating a second zone magneticfield defining a safe zone within the stay-out zone; generating nowarning signal if the only workers in the stay-out zone are in the safezone and at least one vehicle is in or approaching the stay-out zone. 8.A method as in claim 1, wherein the first zone magnetic field oscillatesat less than about 100 kHz.
 9. A multifunctional strip zone (MSZ) devicecomprising: a first MSZ magnetic field generator, including a wireformed into an elongated loop, the loop having a loop length and a loopwidth, the loop length being substantially longer than the loop width, acontrol module adapted to pulse current through the loop to create afirst pulsating magnetic field to define a first zone; a magnetic fieldsensor, including the control module adapted to sense current induced inthe loop, the loop acting as an antennae, at a time when the firstmagnetic field is not being generated, the current being induced by asecond pulsating magnetic field.
 10. A multifunctional strip zone deviceas in claim 9, wherein the first magnetic field has magnetic field linesperpendicular to the length of the loop.
 11. A multifunctional stripzone device as in claim 9, wherein the length of the loop is positionedapproximately horizontally, and further comprising at least oneadditional MSZ magnetic field generator adapted to generate a pulsingmagnetic field that is circular in the approximately horizontaldirection.
 12. A multifunctional strip zone device as in claim 9,wherein the loop length is from about ten feet to about one thousandfeet.
 13. A multifunctional strip zone device as in claim 9, wherein theloop length is from about one hundred feet to about two hundred feet.14. A multifunctional strip zone device as in claim 9, wherein the loopwidth is about one and three quarters inch.
 15. A multifunctional stripzone device as in claim 9, wherein the loop width is from about twoinches to about three inches.
 16. A multifunctional strip zone device asin claim 9, wherein the first zone magnetic field oscillates at lessthan about 100 kHz.
 17. A method of proximity detection, the methodcomprising: generating a first zone magnetic field with a first zonemagnetic field generator defining a first zone, wherein the first zonedefines a controlled area, the boundaries of the controlled area beingat an equal first zone threshold strength of the first zone magneticfield; generating with the first zone magnetic field generator, apattern of magnetic field pulses; generating a vehicle magnetic fielddefining a vehicle danger zone with a vehicle magnetic field generatorassociated with a vehicle, the boundaries of the vehicle danger zonebeing at an equal vehicle threshold strength of the vehicle magneticfield; receiving at the vehicle a worker response signal from a workermagnetic field detector associated with a worker if the strength of thevehicle magnetic field is equal to or above the vehicle thresholdstrength at the worker magnetic field detector, wherein the vehicle isadapted to provide a vehicle alarm based on the worker response signaland the worker response signal is different than the first zone magneticfield; determining, with a vehicle magnetic field detector associatedwith the vehicle, if a strength of the pattern of magnetic field pulses,generated with the first zone magnetic field generator, is equal to orabove the first zone threshold strength at the vehicle magnetic fielddetector; and at least one of (a) causing the vehicle alarm to silence,(b) preventing the activation of the vehicle alarm, and/or (c)decreasing a size of the vehicle danger zone of the vehicle magneticfield generator, each of which if the strength of the pattern ofmagnetic field pulses, generated with the first zone magnetic fieldgenerator, is equal to or above the first zone threshold strength at thevehicle magnetic field detector.
 18. The method of claim 17, furthercomprising, generating a vehicle response signal from the vehiclemagnetic field detector if the strength of the pattern of magnetic fieldpulses generated with the first zone magnetic field generator is equalto or above the threshold strength at the vehicle magnetic fielddetector.
 19. A traffic control system, the system comprising: a firstzone magnetic field generator adapted to generate a first zone magneticfield defining a first zone, wherein the first zone defines a controlledarea, the boundaries of the controlled area being at an equal first zonethreshold strength of the first zone magnetic field, wherein the firstzone magnetic field generator is adapted to generate a pattern ofmagnetic field pulses; a vehicle magnetic field generator associatedwith a vehicle, the vehicle magnetic field generator is adapted togenerate a vehicle magnetic field defining a vehicle danger zone, theboundaries of the vehicle danger zone being at an equal vehiclethreshold strength of the vehicle magnetic field, wherein the vehiclemagnetic field generator is adapted to receive a worker response signalfrom a worker magnetic field detector associated with a worker if thestrength of the vehicle magnetic field is equal to or above the vehiclethreshold strength at the worker magnetic field detector, wherein thevehicle is adapted to provide a vehicle alarm based on the workerresponse signal and the worker response signal is different than thefirst zone magnetic field; a vehicle magnetic field detector associatedwith the vehicle, wherein the vehicle magnetic field detector is adaptedto determine if a strength of the pattern of magnetic field pulses,generated with the first zone magnetic field generator, is equal to orabove the first zone threshold strength at the vehicle magnetic fielddetector; and a first zone controller adapted to perform at least one ofeither (a) cause the vehicle alarm to silence, (b) prevent theactivation of the vehicle alarm, and/or (c) decrease a size of thevehicle danger zone of the vehicle magnetic field generator, each ofwhich if the strength of the pattern of magnetic field pulses, generatedwith the first zone magnetic field generator, is equal to or above thefirst zone threshold strength at the vehicle magnetic field detector.20. The system of claim 19, wherein the vehicle magnetic field detectoris further adapted to generate a vehicle response signal if the strengthof the pattern of magnetic field pulses generated with the zone magneticfield generator is equal to or above the threshold strength at thevehicle magnetic field detector.